The present invention relates to ion beam apparatus and more particularly, to an ion beam apparatus used for processing a sample and a sample processing method.
As a typical example of a conventional ion beam apparatus using a focusing ion beam, a focusing ion beam processing apparatus described in U.S. Pat. No. 2,765,829 has been known. An outline of the apparatus is illustrated in FIG. 23. Ions discharged from ion generating means 201 are focused on a sample 206 by means of focusing means 202 and illuminating means 203. A restriction diaphragm 204 is adapted to determine a beam diameter. In the apparatus, three modes, that is, A, B and C modes are set in accordance with combinations of lens intensity of the focusing means and illuminating means and individual lens voltages in these modes are stored in lens control means 208 and then used. A difference in irradiation position on the sample 206 between the focusing beams in the modes A, B and C is corrected by means of beam deflecting means 205. In the apparatus, beam diameter and beam current of a focusing ion beam used for processing the sample 206 can be selected but only one focusing ion beam being in or assuming a beam focusing state for maximizing image resolution is used as the ion beam for processing.
Also, as a typical example of a processing method noticing beam distribution of the focusing ion beam, a processing method described in JP-A-2-61954 has been known. In the conventional processing method, beam distribution of a focusing ion beam focused on a target is measured through a knife-edge method and simulation is carried out in accordance with measured data to correct the dosage of ions, so that the processing depth can be stabilized to improve reliability of the processing. The processing speed depends on the beam distribution of the ion beam. Accordingly, irregularity in processing depth attributable to a change in beam distribution due to irregularity in voltage set to an electrostatic lens is taken into consideration in order to make the processing depth constant for every processing operation, thereby improving the yield of processing.
As a typical example of an ion beam apparatus using a shaped ion beam, one may refer to an ion beam processing apparatus described in JP-A-9-186138. An outline of the apparatus is illustrated in FIG. 24. Ions discharged from ion generating means 301 by means of a draw-out electrode 302 are changed in beam divergent angle by means of a beam restriction aperture 303. Lens intensity of focusing means 304 is adjusted such that the focal point of a shaped ion beam 313 coincides with a point near the center of projecting lens 307 and lens intensity of the illuminating means 307 is adjusted such that a mask 306 is projected on a sample 309. A focusing ion beam 312 can be obtained by readjusting the lens intensity of the focusing means 304 such that an intermediate focal point of the focusing ion beam 312 coincides with the mask 306, on the basis of an image of the mask 306 that is projected on the sample 309 as a result of scanning of the ion beam on the mask 306 by means of the beam deflecting means 305 and of scanning of the ion beam on the sample 309 by means of beam deflecting means 308.
In the conventional focusing ion beam processing apparatus, the beam current is ten and several nA at the most and the influence of the skirt spread in ion beam distribution does not matter in practice. For the purpose of improving the throughput, an ion beam of larger current is needed but as the current of the ion beam for processing increases, there arises a problem that the skirt spread in beam distribution increases and dullness of a sectional edge portion in a processing region becomes noticeable to prevent realization of high processing position accuracy.
In the processing method described in JP-A-2-61954, the beam distribution is not changed on the basis of a measurement result of beam distribution, that is, the lens voltage is not changed. Further, beam distribution effective to optimize the shape or form of the sectional edge portion in the processing region in accordance with desired processing is not described clearly. Accordingly, any beam distribution effective to permit the sectional edge portion to be processed sharply cannot be obtained, leading to a failure to realize the optimum processing of the sectional edge portion and the high processing position accuracy. Furthermore, simulation is used and much time is therefore required for calculation, raising a problem that high-speed response control cannot be carried out.
In the conventional ion beam apparatus using a shaped ion beam, the shaped ion beam is used for processing to realize high throughput based on large current while maintaining sectional edge sharpness comparable to or better than that obtained with the focusing ion beam but there arise problems that a focusing ion beam for observation cannot be focused and a difference in position develops between the focusing ion beam for observation and the shaped ion beam for processing. The problem that the observation focusing ion beam cannot be focused, that is, the focusing beam diameter increases upon beam switching is avoided by inserting the beam restriction aperture to change the beam divergent angle. The problem of the position difference between the observation focusing ion beam and the processing shaped ion beam is avoided by making the focal point of the focusing ion beam on a stencil mask and moving the mask so as to correct the position difference between the focusing ion beam and the shaped ion beam for processing. But it is difficult to confirm the setting accuracy of the beam restriction aperture necessary to indicate whether the aperture lies on the optical axis of ion beam optical system, leaving a problem of a position difference between the observation focusing ion beam and processing shaped ion beam attributable to insufficient setting accuracy. Besides, two mechanical drive units for the beam restriction aperture and mask are involved to raise a problem that the position difference between the two beams is aggravated. In addition, two mechanisms of the beam restriction aperture and beam deflecting means are needed as components constituting the apparatus.
As described above, in the conventional ion beam apparatus and ion beam processing method using the focusing ion beam, there arises a problem that the processing position accuracy (inclusive of the sectional edge sharpness) is degraded when the beam current is increased to increase the throughput and conversely, the throughput is degraded when the beam current is decreased to increase the processing position accuracy. In the conventional ion beam apparatus using the shaped ion beam, too, the irradiation positions of the focusing ion beam for observation and the shaped ion beam for processing cannot coincided each other with high accuracy and disadvantageously, high throughput can be attained only at the cost of degradation of the processing position accuracy. Furthermore, disadvantageously, the number of components constituting the apparatus is large.